The project's long-term goal is to determine the relationship between mycoplasmas and their eukaryotic hosts. Current emphasis is on elucidating the mycoplasmal surface architecture. Acholeplasma laidlawii whole cell polypeptide profiles, using sodium dodecyl sulfate-polyacrylamide gel electophoresis (SDS-PAGE), have been determined. The profiles are not changed when A. laidlawii is infected with either MVL5l (a filamentous virus) or MVL2 (an enveloped virus). Mycoplasma pulmonis, etiological agent of murine respiratory mycoplasmosis (MRM), is also being studied. A virus, MVMP-l has just been isolated. It has icosahedral head morphology and a possible tail structure. Characterization of MVMP1 and its M. pulmonis host are in progress.